32 
GREENLAND VOYAGE. 
than the air; a sensible evaporation is produced; 
which being condensed as it rises, freezes at the 
same instant, and, being in exceedingly small par¬ 
ticles, is dispersed through the lower parts of the 
atmosphere by the wind, and is productive of the 
most annoying obscurity *. Frost-rime, of the 
greatest density, it is observed, only occurs during 
strong winds, and increases (under similar tem¬ 
perature and humidity of the atmosphere) as the 
turbulence of the sea increases; but if the air be 
calm, it diminishes to a low and thin stratum of 
vapour. I was long in doubt whether the freezing 
of the sprays and froth of the waves, or the eva¬ 
poration of the sea, was the cause of the meteor. 
Having, however, taken a large shallow vessel of 
water into the open air, and placed it in a situa¬ 
tion sheltered from the wind, at a time when the 
frost-rime was particularly dense, the thermome¬ 
ter being at zero, I observed that this water, 
though perfectly still and unruffled, soon began 
to discharge a thin vapour, resembling the frost- 
rime, which it continued to give out, until the 
surface was covered with ice. This experiment 
convinced me that the cause must be simply eva¬ 
poration. 
* See Account of the Arctic Regions, vol. i. p. 434. 
for a more particular description of this meteor. 
